The molding of thermoset polymers is a technologically and commercially important processing technique. In one known version of this technique, a liquid cyclic olefin monomer resin is combined with an olefin metathesis catalyst to form a ROMP composition, and the ROMP composition is added (e.g., poured, cast, infused, injected, etc.) into a mold. The ROMP composition is subjected to conditions effective to polymerize the ROMP composition and on completion the molded article is removed from the mold for any optional post cure processing that may be required. As is known in the art, the liquid cyclic olefin monomer resin may optionally contain added modifiers, fillers, reinforcements, flame retardants, pigments, etc. Examples of such prior art ROMP compositions are disclosed in U.S. Pat. Nos. 5,342,909; 6,310,121; 6,515,084; 6,525,125; 6,759,537; 7,329,758, etc.
ROMP derived polymers have been used to prepare a wide array of commercially important articles including without limitation any molded or shaped article for use as an aerospace component, a marine component, an automotive component, a sporting goods component, an electrical component, and industrial component, medical component, dental component, oil and gas component, or military component. However, primering and painting of ROMP polymer articles is often necessary, particularly when these molded articles are used outdoors, because of their insufficient weathering properties (e.g., oxidation and/or ozone degradation) due to the presence of ethylenic unsaturation throughout the body and surface of the ROMP polymer.
Typically, in order to improve the weathering properties of ROMP molded articles by painting, the surface of the article may have to be sanded and wiped with a solvent (e.g., 2-propanol, soapy water, etc.) to remove any residual mold release and/or dirt on the surface as a result of manufacturing and/or handling. The article is then treated with a primer treatment and/or a subsequent paint treatment. When the article is first treated with a primer treatment, the second or subsequent paint treatment is often referred to as a top-coat. Unfortunately the application of primer and/or paint (e.g., a paint top-coat) to a demolded ROMP polymer article is a difficult, expensive, and time consuming process. In order to prime and paint a molded ROMP polymer article, it is typically necessary to have a paint booth or clean room to avoid unwanted airborne contaminants such as dirt, dust, oils, etc. The presence of such unwanted airborne contaminants often results in the quality of the primered and/or painted surface (e.g., top-coat paint surface) being unacceptable due to the formation of pinholes and other surface defects present in the primered and/or painted surface. Moreover, the primering and/or painting of ROMP polymer articles typically requires skilled personnel who are experienced and knowledgeable in the art of applying primer and/or paint to polymer surfaces, resulting in additional cost being added to the final primered and/or painted ROMP polymer article.
Generally, it would be useful and commercially important to be able to provide a molded ROMP polymer article that does not need to be primered and/or painted after being demolded. Therefore, it would be useful and commercially important to be able to apply a primer and/or paint to the surface of a molded ROMP polymer article while the molded ROMP polymer article is still in the mold instead of after demolding. Such processes are common practice in the molding of fiber reinforced plastics, such as fiberglass reinforced composites comprising polyester resin or vinyl ester resins as well as in the molding of polyurethane polymers and are commonly known in the art as gel-coating, in-mold coating, and/or in-mold painting. In particular it would be useful and commercially important to be able to provide an in-mold coated ROMP polymer article where the primer and/or paint is urethane, acrylic, or epoxy based. More preferably, it would be useful and commercially important to be able to provide an in-mold coated ROMP polymer article where the primer and/or paint is urethane based. As is commonly known in the art, urethane based primers and/or paints are typically preferred over acrylic and epoxy based primers and/or paints. Epoxy paints, particularly when used as a top-coat, are known to develop a chalky film on the exterior when exposed to ultraviolet light; therefore, when epoxy paint is used as the top-coat it is often recommended for use in indoor applications or applications where high gloss and/or original color retention are not required. Moreover, epoxy based paints may be suitable for industrial applications and applications in corrosive environments. On the other hand, urethane based paints have superior performance and retention of gloss and color when exposed to ultraviolet light. Therefore, urethane based paints and/or primers are preferred over epoxy based paints and/or primers for outdoor applications. Acrylic paints differ from urethane paints in that acrylic paints are water based, where urethane paints are solvent based. While the water based nature of acrylic paints makes them less toxic than urethane based paints, the drawback is that acrylic based paints being water based take significantly longer to dry (i.e., cure) than urethane paints. Therefore, the use of acrylic based paints is not particularly conducive to the molding of ROMP polymer articles, where it is advantageous to have short cycle times to reduce the cost of the finished ROMP polymer articles. Moreover, urethane paints are preferred for many applications and are the industry standard for automotive paint, where high gloss and color retention are a requirement. Therefore, it would be particularly useful and commercially important to be able to provide an in-mold coating system for use with molding ROMP polymer articles where the primer and/or paint is urethane based.
Previously, there have been few methods for in-mold coating of ROMP polymers. One method for in-mold coating of ROMP polymers is disclosed in International Application Nos. WO 2005/046958 A1; WO 2006/070813 A1; WO 2006/118206 A1; WO 2007/086444 A1; and WO 2007/125787 A1. According to these disclosures a ROMP composition is first added to a mold and subjected to conditions effective to polymerize the ROMP composition to form a ROMP polymer article. Once the ROMP polymer article is cured in the mold, the mold is opened some minimal amount to create a gap between the molded article surface(s) and the mold surface(s) and a coating material is injected or poured into the gap, where the coating material flows around the molded article thereby coating the surface(s) of the ROMP polymer article. This method of coating a molded ROMP polymer article suffers from a number of limitations. One major limitation of this method is the difficulty of obtaining a uniformly coated molded article, particularly where the shape of the molded article possesses a complex geometry. Moreover, this methodology also requires the use of a coating material having a composition containing an ethylenic unsaturated monomer, a polymerization component, a mold release agent and an organic-peroxide initiator, where the organic-peroxide initiator is required so as to effectuate adhesion between the coating material and the ROMP polymer.
Another method for in-mold coating of a ROMP polymer is disclosed in U.S. Pat. No. 5,098,750. According to this disclosure a polymer which is capable of forming a film on the mold surface is dissolved in a solvent, and the solvent/polymer mixture is applied to the mold surface, the mold is closed, a ROMP composition is added to the mold, and the ROMP composition is subjected to conditions effective to polymerize the ROMP composition. While this method may lead to reasonable bonding via interface blending or mechanical bonding between the polymer surface and the polymer film, the overall quality and degree of adhesion between the polymer film and the ROMP polymer over time is questionable. Moreover, this method requires the use of large amounts of volatile organic solvents to dissolve the polymers used to form the polymer film, where the use of these organic solvents creates elevated workplace volatile organic content (VOC) levels, which in recent years has come under strict regulation by federal and state agencies. While this method is a pre-molded coating procedure there is no discussion related to the use of commercially available low VOC based primer(s) and/or paint(s).
Therefore, despite advances achieved in the art, particularly in properties of olefin metathesis polymers (e.g., ROMP polymers) and their associated applications, a continuing need therefore exists for further improvement in a number of areas, including methods and compositions for in-mold coating of ROMP polymer articles.